All eight matches in fourth-round play of the Lamar Hunt U.S. Open Cup are set for tonight. Here’s what you need to know, starting with the basic schedule (courtesy of a screen grab from U.S. Soccer):

The lowdown on tier-vs.-tier: What makes the Open Cup so great is the upset potential, which naturally dwindles as the rounds progress. As such, only four of tonight’s eight matches feature the lower tier sides vs. MLS clubs.

“Low” men standing: Orlando City and the Charleston Battery are part of the USL Pro league, domestic soccer’s officially sanctioned third tier. The Tampa Bay Rowdies and Carolina Railhawks are NASL clubs, soccer’s second tier. The other eight clubs are from Major League Soccer, the country’s top tier.

The top potential for upset: The Carolina Railhawks have already dispatched Major League Soccer’s champions, the LA Galaxy, which had dispatched a reserve squad for the teams’ third round match. Now, in the very same ground in Cary, N.C., the Railhawks have a chance to send another team back to Southern California in a heap of disappointment. Chivas USA visits Carolina, and we can’t even be certain all the best Goats’ players will be available.

The local derbies: League-leading FC Dallas meets Houston in North Texas. It’s a sticky one for Schellas Hydman’s FCD because of a big match just three nights later. Houston, with this weekend off, is more free to play its best lineup.

Meanwhile, New York and New England meet at Harvard’s Soccer Field, putting a Cup spin on their rivalry. And they are playing in the city! In an intimate venue, and here’s why. Not that anybody needs to explain; we love smaller venues for Open Cup matches.

Speaking of smaller venues …: Too bad only one of the lower tier sides will host tonight. But the WakeMed Soccer Park (pictured at right) does have that Open Cup feel, doesn’t it.

Dom Dwyer is under contract for Sporting Kansas City, a 22-year-old English striker who has done so well on loan this year for the Orlando City Lions. As those teams happen to be playing, and as Orlando is a Kansas City affiliate, the players aren’t being allowed to participate tonight at Sporting Park. Dwyer is one of four such SKC loanees who are benched for this one.